PT-symmetric transport in non-PT-symmetric bi-layer optical arrays

We study transport properties of an array created by alternating $(a,b)$ layers with balanced loss/gain characterized by the key parameter $γ$. It is shown that for non-equal widths of $(a,b)$ layers, i.e., when the corresponding Hamiltonian is non-PT-symmetric, the system exhibits the scattering properties similar to those of truly PT-symmetric models provided that without loss/gain the structure presents the matched quarter stack. The inclusion of the loss/gain terms leads to an emergence of a finite number of spectral bands characterized by real values of the Bloch index. Each spectral band consists of a central region where the transmission coefficient $T_N \geq 1$, and two side regions with $T_N \leq 1$. At the borders between these regions the unidirectional reflectivity occurs. Also, the set of Fabry-Perrot resonances with $T_N=1$ are found in spite of the presence of loss/gain.

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